What you're describing sounds like it's working as expected though. Check the instructions at the top - they are probably telling you to keep making selections until none remain and then press the Verify button.
In those cases, the user will get new images after making selections. If those new images match what the instructions say to select then select them again, but if they do not then do not select the newly added image again.
Once you've cleared out all the images matching the instructions, then you would press the verify and you will have satisfied the reCAPTCHA.
If you feel that you're being presented with more complicated reCAPTCHA challenges than you should be then you should make sure that you are using the latest version of your browser and that you have scripting enabled. Also make sure you don't have any special settings that you've put in place for the site that you're accessing (IE's compatibility mode is an example of a setting that would cause you to have more difficult reCAPTCHA callenges).
-Seth